The search for speed in temperature measurement is an unending quest, especially, but not exclusively, in measuring human body temperature. Examples of persons and situations wherein there is a need to obtain quick temperature readings include, inter alia, a physician in an emergency room evaluating the status of a patient, a chef determining whether the interior of a food (e.g. meat) has attained a desired temperature, an HVAC technician checking the air temperature in an air duct, and a mother determining whether her screaming child has a fever. Each of these situations requires that a temperature measurement be obtained in a relatively quick manner.
Traditionally, temperatures (whether of a human, food product or air) were determined using a mercury-in-glass thermometer. This type of thermometer typically requires approximately three (3) minutes to achieve a stable reading. Recently, however, advances have been made to reduce the time required for a thermometer to achieve a stable temperature reading. These advances are most often embodied in low-cost digital fever thermometers which allow for relatively fast temperature detection by the use of a temperature sensor having a relatively low mass and heat capacity.
Digital thermometers typically display a stable temperature reading in half the time required for that of traditional mercury-in-glass thermometers. Recently, infrared thermometers have been developed which attain an even faster stable temperature reading as compared to digital thermometers. This is generally accomplished by measuring the infrared emissions of the tympanic membrane and the ear canal. The infrared thermometers, however, are less accurate than the traditional contact type thermometers and are subject to variability of use, variability of ear canal shape, and inter-ear temperature differences.
One specific approach to quick temperature detection is disclosed in U.S. Pat. No. 4,183,248 to West which teaches reducing heat loss through the thermometer stem by activating a heater in the stem to match the temperature of the temperature sensor. The West patent mentions a 30-second response time using this method. While the heat loss through the thermometer stem is compensated for by the heat produced by the heater, the heat capacity of the sensor tip causes a local cooling on the area of the body which is in contact with the sensor tip, and time is required to replenish the heat loss to this area of the body to obtain an accurate temperature reading.
Another approach to quick temperature detection is disclosed in U.S. Pat. No. 5,632,555 to Gregory wherein a heater is employed to reduce heat capacitance. Gregory teaches heating the thermometer sensor tip to a predetermined temperature of 95.degree. F. before insertion of the tip in the patient's mouth. Thereafter, a temperature rise profile is used to calculate (that is, estimate or predict) a terminal (that is, final stable) temperature. Gregory discloses predicting the terminal temperature in 4 seconds. However, prediction is subject to numerous factors such as insertion time, movement, and pressure variability. In addition, when probe covers are utilized, variations in probe cover thickness and mass must be considered in the prediction routine.